Coming: Self-cleaning glass and super-slick surfaces

March 3, 2005
Ohio State University (OSU) engineers are designing superslick, water-repellent surfaces that could lead to self-cleaning glass.

The patentpending technology could also reduce friction between tiny moving parts inside microdevices.

The technology creates a surface that mimics the texture of lotus leaves. Scientists have long known that the lotus, or water lily, makes a good model for a water-repellent surface. The leaf is waxy and covered with tiny bumps, so water rolls off.

In studying the lotus leaf, OSU engineers saw they could exploit the same texture to reduce friction between moving parts on machines. Small machines, such as those under development in the fields of micro and nanotechnology, can't be lubricated by normal means.

In general, what's good for water repellency is good for fighting friction. But when it comes to designing high-tech surfaces such as waterrepellent car windshields or low-friction joints on micromachines, merely copying a lotus leaf isn't enough. Bumpy, waxy surfaces can actually become sticky under some circumstances. So OSU researchers have built the first computer model that calculates the best bumpy surface for different materials and applications.

So far, the OSU team is focusing on modeling bumps of different sizes and shapes. All the bumps included in the model aid water repellency by keeping water droplets from directly touching the surface.

The bumps are packed close together and are much smaller than a droplet so they can't puncture the droplet. In fact, if the droplet were perfectly balanced, it would just lie on the bumps the way a person can safely lay on a bed of nails. The computer model calculates how and where to place the bumps so the droplet will touch the surface in just the right way to roll off.

Because the bumps are only a few nanometers wide, glass textured with them would still be transparent. Automobile windshields and residential windows are among the possible uses. But the OSU team is most excited about applications in microelectronics. The technique looks promising as a way to reduce the friction between moving parts inside micromachines. In light-based electronics where tiny mirrors move to reflect light in different directions, for example, the moving parts are too small to use traditional lubricants.

One way to eliminate the need for lubricant is to build slick surfaces onto each individual part. The lotus-leaf surfaces might do the job. Manufacturers would use the OSU model to figure out the size and shape of bumps that would work best.

The OSU researchers say they are looking for an industrial partner to carry the work further.

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